KAIST’s RAIBO2 quadruped completed the 42.195-kilometre Sangju Dried Persimmon Marathon in 4 hours, 19 minutes and 52 seconds on one battery charge. The race took place in November 2024; a paper published in Nature on September 23, 2026, explains the design behind the finish.
Legged robots spend energy holding their weight over moving joints, and each foot strike can shed kinetic energy. The KAIST team analysed losses across the whole machine instead of trying to improve only its battery, motors or gait.
The team targeted losses in the legs, electronics and gait
The paper links RAIBO2’s efficiency to three changes: a lightweight, force-transparent leg mechanism; a low-resistance motor-driver circuit; and a locomotion policy designed to cut mechanical and electrical losses. Here, force transparency means the legs transmit external forces with less resistance inside their joints.
Stress analysis guided material removal from leg components, while bench measurements helped the team compare motor-driver designs. The paper reports reinforcement-learning tests that accounted for energy losses from actuator heating and foot-ground impacts.
The marathon tested endurance, not autonomous route planning
The study reports a cost of transport (COT) of 0.25 for RAIBO2 and cites 0.37 as a human benchmark. COT normalizes energy use for weight and distance, so the figures compare transport efficiency rather than race times or total energy use. The paper also reports more than three times the range per charge of existing quadrupeds; its supplementary comparison draws on figures compiled from previous studies and public sources, not a same-course contest.
KAIST’s November 2024 event announcement described autonomous navigation as follow-up research. The paper documents RAIBO2 completing the course on one charge; it does not establish independent route planning.
Sources
- Lee et al., “A quadruped robot designed to complete a marathon on a single battery charge,” Nature (September 23, 2026)
- KAIST News Center, RAIBO2 completes the Sangju marathon (November 17, 2024)
- KAIST RAI Lab, RAIBO2 marathon and energy-use dataset (Zenodo)
Image: Boston Dynamics’ Spot photographed by Jonte in 2023. Wikimedia Commons, CC BY-SA 4.0. This illustrative image does not depict KAIST’s RAIBO2. Original photo and license.